Questions tagged [sequence]
For challenges involving sequences, typically of numbers following some pattern.
977 questions
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A yet-unlisted sequence
I was looking for a simple sequence that's not yet referenced on the OEIS and came up with this one(*):
\$a_1=2\$
\$a_2=3\$
For \$n>2\$, \$a_n\$ is the smallest number of the form \$a_i\times a_j+...
- 205k
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IMO 2025: Divisor sums that go forever
Problem 4 of the 2025 International Mathematical Olympiad asked (paraphrased):
Let \$f(n)\$ be the sum of the largest three proper divisors of \$n\$,
that is divisors excluding \$n\$ itself. For ...
- 149k
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Locate \r\n\r\n in a HTTP/1.1 POST request
Given an HTTP/1.1 POST request represented as a buffer (e.g., Uint8Array; uint8_t) of bytes, ...
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Triangular Transposition Cipher
A text that can be arranged triangularly in some fashion can be read back in some other fashion effectively enciphering it.
Narrowing down a set of plausible triangular numberings allows to ...
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Putting the pieces together
In this code-golf challenge, you will count the number of ways of putting together pieces of a building toy which consists of slotted squares that interlock with one another, shown below. In ...
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Output the Echo Numbers
Echo numbers (A383896) are positive integers k such that the largest prime factor of k-1 is a suffix of ...
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Is it a product of 4 unique primes (A046386)?
A046386 is the sequence of all natural numbers that are the product of exactly 4 distinct primes.
Write the shortest program, function, or code snippet, that, when given a natural number, outputs ...
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Ruler-and-compass constructions
In this code-golf challenge, you will work with a construction that was used by the ancient Greeks: the straightedge-and-compass construction. In particular, you will count how many different ...
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A121016: Numbers whose binary expansion is properly periodic. or A328594: Numbers whose binary expansion is aperiodic
I have been studying how to compress the Dis programs into their equvalent ones. One of the possibly easiest subset is programs with only } and ...
- 1,267
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Counting Gessel walks
OEIS A135404 gives the number of Gessel walks \$g(n)\$ of length \$2n\$. A Gessel walk is
a walk on the square lattice starting and ending at the origin
with possible steps (1,0), (-1,0), (1,1), (-1,-...
- 4,739
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Repetition-restricted strings
Given an alphabet size, \$n>0\$, and an occurrence limit, \$k>0\$, produce the number, \$a(n, k)\$, of strings that may be constructed from the \$n\$ letters in the alphabet which have no more ...
- 115k
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Number of legal positions in 1D go
A 1D go position on a board of size n is a sequence of length n consisting of the numbers0, <...
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How many chains?
Given a positive integer \$n\$, a partition of \$n\$ is an ascending sequence of numbers that sum to \$n\$.
Given two partitions \$a\$ and \$b\$, \$a\$ is a refinement of \$b\$ iff \$b\$ can be ...
- 103k
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Meandering over ℤ
The easiest way to understand this task is to look at this
graph,
which you can change interactively.
It defines a sequence n -> a(n) like this:
a(0) = 0; thereafter a(n) is the least integer (in ...
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Counting Rota-Baxter words
A Rota-Baxter word, \$w\$, is a string made of the symbols a, (, and ) such that the ...
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